A195613 Numbers n with property that n, 2n-1 and 2n+1 are composite.

25, 28, 32, 38, 46, 58, 60, 62, 72, 77, 80, 85, 88, 92, 93, 94, 102, 104, 108, 110, 118, 122, 123, 124, 130, 133, 143, 144, 145, 148, 150, 152, 160, 161, 162, 164, 170, 171, 172, 178, 182, 185, 188, 196, 202, 203, 206, 207, 208, 212, 213, 214, 218, 226, 235

Offset

1,1

Comments

In A000027, if n, n+(n-1) and n+(n+1) are composite, then n is a term of this sequence.

Suggestion: there are arbitrarily long sets of consecutive integers, e.g., 632..637, 665..672, 6428..6443.

Links

Table of n, a(n) for n=1..55.

Mathematica

Select[Range[2, 1000], !PrimeQ[2#-1]&&!PrimeQ[#]&&!PrimeQ[2#+1]&]
Select[Range[250], AllTrue[{#, 2#-1, 2#+1}, CompositeQ]&] (* Harvey P. Dale, Feb 26 2022 *)

Crossrefs

Sequence in context: A345509 A295748 A254226 * A127652 A303812 A334534

Adjacent sequences: A195610 A195611 A195612 * A195614 A195615 A195616

Keyword

nonn

Author

Zak Seidov, Sep 21 2011

Status

approved